Ongoing debates about the need to deeply transform energy systems worldwide have spurred renewed scholarly interest in the role of future-visions and foreknowledge in energy policy. Forecasts and scenarios are in fact ubiquitous in energy debates: commonly calculated using energy models, they are employed by governments, administrations and civil society actors to identify problems, choose between potential solutions, and justify specific forms of political intervention. This article contributes to these debates through a historic study of foreknowledge-making – modelling, forecasting, and scenario-building – and its relationship to the structuring of ‘energy policy’ as an autonomous policy domain in France and Germany. It brings together two strands of literature: work in the anthropology of politics on ‘policy assemblages’, and STS research on the ‘performative’ effects of foreknowledge. The main argument is that new ways of assembling energy systems in energy modelling, and of bringing together policy networks in scenario-building and forecasting exercises, can contribute to policy change. To analyse the conditions under which such change occurs, the article focuses on two periods: the making of national energy policies as ‘energy supply policies’ in the post-war decades; and challenges to dominant approaches to energy policy and energy modelling in the 1970s and 1980s. It concludes by arguing that further research should not only focus on the effects of foreknowledge on expectations and beliefs (‘discursive performativity’), but also take into account how new models ‘equip’ political, administrative and market actors (‘material performativity’), and how forecasting practices recompose and shape wider policy worlds (‘social performativity’).